This invention relates to a device to carry out the heating of fluids to a predetermined temperature and, more particularly, to a device that can efficiently heat medical fluids for introduction into a living entity such as an animal or a human patient.
In general, there are certainly many methods and devices for heating fluids including the use of resistance heaters as well as combustion heaters, heat exchange units and the like. One type of heater that has been disclosed for use in heating of fluids is by means of a transformer having a primary and a secondary. Basically, in such devices, the secondary comprises a conduit through which the fluid to be heated passes and that secondary is shorted out so as to convert the magnetic flux created by an alternating current through the primary into heat in the secondary. Accordingly, as the fluid passes through the secondary, it is heated and can be used for various purposes. A transformer type of fluid heater is shown and described in U.S. Pat. No. 6,078,032 of Miller et al where the heating device is utilized to heat water in the preparation of coffee.
In the field of medical uses, heaters are normally used to warm a fluid for infusion into a living being, albeit a human patient or an animal. Typically, the fluid used in such practice are fluids such as plasma, whole blood for trauma use, fluids needed during organ transplants, frozen plasma that needs to be heated up and the like. With the introduction of these fluids into a living being, it is obvious that there is a need for precise control of the temperature as well as to be able to maintain that temperature constant during different flows of the fluid and even during the stoppage of that flow, that is, the temperature must be controlled even during a stoppage of the flow within the heater so that no excessive temperatures are reached during any conditions of the flow or operation of the heating device including, during a cycle where the flow is halted for a period of time and then restarted.
In addition, the heater for such uses must provide a uniform heating to the fluid itself as any hot spots or areas where an excessive temperature may contact the fluid can cause a degrading of the fluid and render that fluid unfit for the intended purpose. For example a hot spot may give rise to an excessive temperature and can destroy protein that is in the fluids being delivered. In addition, of course, it is important in the use of such heater devices for medical uses that the surfaces or any materials that come in contact with the fluids circulating to and from the patient be capable of being easily sterilized in preparation for subsequent patients and to prevent cross contamination. Certainly, in the aforedescribed Miller et al patent, there is no practical way to facilitate such cleaning and sterilization process with that disclosed heater device.
Accordingly, it would be advantageous to provide a heater of such fluids that is efficient, safe for use without fear of electrical shock, provide an even, uniform heating of the fluid and yet have sufficient capacity to heat the fluid to the desired temperature at the flows utilized in that use.
Thus, in accordance with the present invention, there is provided a heating device for the heating of fluids that provides a uniform heat to the fluid and can be operated at the precise temperatures needed for warming a supply of fluid to be used for the infusion of an entity including a living animal or human. In the present invention the heater itself is a transformer where the secondary includes a path for the flow of the fluid. The preferred transformer core comprises two E-shaped ferrite core sections that meet together with the open ends of the E-shaped core sections coming together. The E-shaped configuration provides two outer legs and an inner leg of each of the E-shaped core sections and the inner legs are shorter that the outer legs of each core section. There is an opening formed in-between the two E-shaped sections of the primary due to the shorter length of the inner leg of the of the E-shaped core sections.
The primary windings are wound around both of the E-shaped core sections equally, that is, there are preferably an equal number of windings around each of the E-shaped core sections and a wire loop connects the two sets of windings. In the preferred embodiment, both E-shaped core sections are biased toward each other. Ferrite blocks are also preferably located adjacent and in contact with the external sides of the E-shaped core sections in order to made sure there is continuity between the core sections even when the outer legs of the core sections are not fully in contact with each other. By passing a high frequency electrical current through the primary, an alternating magnetic field is created in the secondary.
The secondary of the transformer comprises a planar singular, elongated tubular loop having an inlet and an outlet and a plurality of curves and corners to break up any laminar flow pattern of fluid to insure a thorough mixing of the fluid, thereby creating a isothermic fluid flowing from the outlet at the desired elevated temperature. Each curve is formed to have an increased diameter in order to slow the velocity of the fluid passing through the curves and to reduce the hydraulic gradient formation.
The secondary itself is a high resistivity, thin walled ferrous material and is encased within a plastic material preferably polyetheramide to form a cartridge that can be easily inserted and removed from an operative position in the opening formed between the two core sections. The material of the secondary is preferably stainless steel. The elongated loop is shorted out at or near the inlet and outlet by welding in order to convert the magnetic flux created by the high frequency primary into heat in the secondary.
By the use of the aforedescribed construction, the plastic encased secondary can be removed from the E-shaped core sections for cleaning, such as autoclaving, and the secondary returned to the position within the opening between the core sections, or an alternate secondary cartridge can be inserted while the other secondary cartridge is being cleaned or repaired.
A ferrite inset is also incased in the plastic along with the secondary and is located in the inner area of the elongated looped configuration of the secondary. The addition of the ferrite insert aids in the uniform distribution of the magnetic flux and thus enhances the heating effect of the overall device. When the secondary is inserted into the opening as the heat device is functioning, the bias forcing the two core sections together to assure that the secondary is retained in close proximity to the ferrite core sections to aid in the efficiency of the device.
The interior surface of the secondary is preferably coated with and hermetically sealed by a layer of a material bonded to that surface. The material has a high dielectric insulation, has a low potential for triggering an immune response and has very low thrombogenic properties. In the preferred embodiment, the coating material is a vacuum deposited layer of parylene.
These and other features and advantages of the present invention will become more readily apparent during the following detailed description of the invention taken in conjunction with the drawings herein.